As is known to those skilled in the art, the so-called burning thermoplastics which include, for example, polystyrene, the polyolefins, polymethyl methacrylate and the ABS resins, all possess the undesirable property, upon being ignited, of continuing to burn until substantially consumed. Accordingly, these hard and, in many instances, optically clear materials which are widely employed for the preparation of a broad range of consumer and industrial articles cannot, ordinarily, be used in many applications involving their use in building interiors or in products which will be subjected to prolonged exposure to high temperatures. Thus, the burning thermoplastics fail to display fire or flame retardant properties which would, otherwise, permit them to either meet the standards set by various building codes or to be safely employed in place of more costly materials.
Prior attempts to provide fire retardant compositions from these burning thermoplastics have involved their blending with a variety of extraneous additives such, for example, as antimony oxides, halogenated paraffins, halogenated hydrocarbons and low molecular weight phosphate esters. Many of these additives, such as antimony trioxide, are quite expensive while, in general, their effective utilization requires their presence in rather high concentrations which adversely effect the physical properties of the treated polymers. Thus, the inherent hardness and, in some instances, the clarity of the thermoplastic polymers are particularly prone to deterioration in the presence of the high concentrations of these additives which are necessary in order to achieve a self-extinguishing polymer composition.
It is, therefore, the prime object of this invention to provide novel fire retardancy additives which can be used, per se, as fire retardant materials or which can, preferably, be admixed with burning thermoplastics so as to yield polyblends characterized by their excellent fire retardant properties which are achieved without any serious diminution of the physical properties of such blends. Various other objects and advantages of this invention will be apparent from the disclosure thereof which follows hereinafter.